Refer to FIG. 1, the conventional power control technology, such as the dimming control, usually adopts an ON-OFF Interval modulation method, wherein the ratio of an ON interval and an OFF interval is modulated to vary the energy output. It is the most frequently-used method. In the above-mentioned method, there is an EDR (Excitation Dynamical Ratio) defined as
                              ≈                                                    E                1                            ⁡                              (                                  energy                  ⁢                                                                          ⁢                  of                  ⁢                                                                          ⁢                  ON                  ⁢                                                                          ⁢                  interval                                )                                                                    E                2                            ⁡                              (                                  energy                  ⁢                                                                          ⁢                  of                  ⁢                                                                          ⁢                  OFF                  ⁢                                                                          ⁢                  interval                                )                                                    ,                            (                  Equation          ⁢                                          ⁢          1                )            and the traditional EDR is
            E      1                      E        ⁢                                  ⁢        2            ≈      0        ⇒      ∞    .  
The above-mentioned equation will attain an EDR of infinity, and the effect of the infinite EDR can be explained with the following analogy example: a steel wire is bent by 90 degrees, and restored to be a straight wire, and then bent by 90 degrees again; after the above-mentioned steps are repeated many times, the steel wire will be fractured finally; if the steel wire is bent by only 10 degrees, much more times of bending is required to fracture the steel wire. Similarly, when LED works in two extremities, it will age faster. Therefore, the conventional power control technology of too high an EDR greatly affects the lifetime of LED.